Development of a scaled STATCOM prototype based on 21-level cascade H-bridge inverter

This paper is intended to present a laboratory scaled STATCOM prototype using 21-level cascade H-bridge inverter, which is developed to verify the control schemes that will be adopted in a plusmn50 MVar STATCOM project. A novel multi-pulse optimal PWM technique for STATCOM based on cascade H-bridge inverters is proposed. The harmonics are suppressed using optimization techniques. Furthermore the fundamental output voltages of all the inverter cells are controlled to be equal to make them equally share the exchanged power with power system, which is to maintain the DC voltages as balance as possible. Combined with the switching-pattern swapping technique, the DC voltages can be fairly balanced. The redundant operation is achieved through storing switching angles for various cases of N. A nonlinear control scheme based on the theory of exact linearization via feedback is proposed to improve the dynamic performance of the STATCOM. The validity of the proposed method is verified using the experimental results of the laboratory scaled prototype